Research studies on a wide variety of industrial and laboratory organic chemical compounds have led to the development of a new high-quality, sulfur-phosphorus rear axle lubricant. Through extensive use of bench-type screening tests, new technology was developed to provide a formulation with exceptional anti-rust performance as measured by the CRC L-33 Test. Other outstanding features include EP protection, long-term copper corrosion protection capabilities, foam control, and thermal oxidation stability. The additive components may be used in mineral oils or synthetic fluids where extreme weather operation is desired. The formulation may also be used with extremely shear-stable viscosity index improvers to formulate multigrade rear axle lubricants.